Silver molybdate

Silver molybdate (Ag₂MoO₄), a chemical compound, is a yellow, cubic crystalline substance often used in glass. Its crystals present two types of electronic structure, depending on the pressure conditions to which the crystal is subjected. At room temperature, Ag₂MoO₄ exhibits a spinel-type cubic structure, known as β-Ag₂MoO₄, which is more stable in nature. However, when exposed to high hydrostatic pressure, the tetragonal α-Ag₂MoO₄ forms as a metastable phase.

Synthesis and properties

Research published in 2015 reported the formation of α-Ag₂MoO₄ by solution-phase precipitation under ambient conditions, using 3-bis(2-pyridyl)pyrazine (dpp) as a doping agent. The influence of the pH of the starting solution on the growth and formation processes of distinct heterostructures (brooms, flowers and rods) was investigated by Singh ''et al''. and Fodjo ''et al''., in which sodium borohydride was employed to induce the reduction of silver nanoparticles on the surface of Ag₂MoO₄ crystals in order to enhance Raman scattering. In other studies, Ag-Ag₂MoO₄ composites prepared by microwave-assisted hydrothermal synthesis presented interesting photocatalytic activity for the degradation of rhodamine B under visible light. In addition, Ag₂MoO₄ mixed with graphite acts as a good lubricant for Ni-based composites, improving the tribological properties of this system. Different synthetic methods have been employed to obtain pure β-Ag₂MoO₄ crystals, including solid-state reaction or oxide mixture at high temperature, melt-quenching, and Czochralski growth. Particularly, high temperatures, long processing times, and/or sophisticated equipment are necessary in these synthetic routes. Moreover, the final products may be composed of irregular particle shapes with nonhomogeneous size distribution as well as contain the presence of secondary phases. In recent years, pure β-Ag₂MoO₄ crystals have been synthesized by co-precipitation, microwave-assisted hydrothermal synthesis, a dynamic template route using polymerization of acrylamide assisted templates, and an impregnation/calcination method.

In 2015, the literature reported the formation of β-Ag₂MoO₄ crystals using different chemical solvents in the reaction medium. These β-Ag₂MoO₄ microcrystals were synthesized by the precipitation method, employing several polar solvents: deionized water (H₂O), methanol (CH₄O), ethanol (C₂H₆O), 1-propanol (C₃H₈O) and 1-butanol (C₄H₁₀O) at 60 °C for 8 h. X-ray diffraction (XRD), Rietveld refinements and field emission scanning electron microscopy ( FESEM) were employed in structural and morphological characterizations. Moreover, some researchers have investigated new ways to improve the photocatalytic properties of β–Ag₂MoO₄ crystals through hydrothermal processing at different temperatures (100, 120, 140 and 160 °C) for 2 h and replacement of Ag atoms by Zn to formation of silver zinc molybdate ²â€“(Ag_2−2xZnx)MoO₄microcrystals by a sonochemical method at 30 °C for 3 h. These new crystals were able to degrade the organic cationic dye rhodamine B and the anionic dye Remazol Brilliant Violet 5R7>

References

{{Molybdates

Silver compounds
Molybdates